This invention relates to a prefabricated prosthetic replacement for a temporomandibular joint (TM Joint) disc in the human jaw.
In dentistry, there is a newly emerging specialty which treats Craniomandibular-Cervical Pain Dysfunction Syndrome. This syndrome is a neuromuscular and musculoskeletal dysfunction which is responsible for producing symptoms as diverse as facial pain, headaches, neckaches and locking of the jaw. Additional symptoms may be ringing in the ears, unilateral deafness, blurry vision, photophobia, nausea and dizziness. Because the syndrome produces symptoms which are so diverse, we organize them into a triad of dysfunctions in the cervical spine, the muscles of the head and neck, and the temporomandibular joint.
The Temporomandibular Joint Pain Dysfunction Syndrome occurs following pathological stretching, tearing and trauma to the ligaments and soft tissues of the TM Joint. Stretching and tearing of ligaments leads to pathological repositioning of the TM Joint disc and the symptoms that originate from the joint are pain and limitation of opening the mouth.
Since an apparent function of the disc is to provide stability within the joint, the various pathological changes that occur may result in destabilization of the joint. The disc may no longer be available to cradle the condyle and maintain contact between the condyle and the posterior slope of the eminence. To compensate for lost stability, the muscles of mastication, i.e., the masseters, temporalis, internal and external pterygoids, are thought to add stability by increasing their state of constant contraction (tonus). The additional contraction of the muscles may lead to facial pain, headaches, and neckaches of muscular origin.
Therefore, when Temporomandibular Joint Pain Dysfunction Syndrome is present, treatment may be indicated to reduce pain and dysfunction. Conventional wisdom dictates that conservative treatment in the form of bite appliances to reposition the condyle, physical therapy, and medications are the treatment of choice. However, there are patients who have undergone appropriate conservative therapy and have not been helped. For these patients, surgery may be indicated.
Attempts to treat the temporomandibular joint surgically have had limited success.
Condylectomy, or removal of the mandibular condyle, is a surgical procedure based upon the assumption that pain and dysfunction originate from the condyle. Experience with this procedure has shown that it may increase pain by changing the anatomical alignment of the mandible, causing a unilateral shift towards the side with the reduced condyle. This destabilizes the joint further and causes muscle imbalance that leads to muscle pain.
Disc plication is another surgical procedure based upon the assumption that an anteriorly displaced TM Joint disc destabilizes the joint and leads to further joint damage and muscle pain. The procedure removes the stretched posterior ligament and repositions the disc into a more physiologic position. Sutures are used to maintain the disc in the new position. When indicated, this procedure effectively treats anterior disc displacement. However, the procedure is most useful only during early stages of internal derangement when non-surgical therapy is preferable.
Since the surgeon is often called upon to treat the more advanced cases of internal derangement, removal of the TM Joint disc is sometimes needed. Some surgeons remove the TM Joint disc and do not replace it with a prosthetic implant. Non-replacement of the TM Joint disc leads to instability in the joint, the mandible, and dental malocclusion. It also subjects the TM Joint to osteoarthritic changes as a result of friction during motion.
Removal of the disc has often been followed up with implantation of a prosthetic disc to avoid complications. To date, all known prosthetic discs have yielded complications as a result of their usage. Two types of prosthetic discs have been surgically implanted composed of PROPLAST, which is a polytetrafluoroethylene-carbon composite and SILASTIC, a polydimethylsiloxane. These materials are relatively hard and the prosthetic discs formed from these materials are wired into place. Wiring is traumatic and sometimes fails to stabilize the implant. As a result the implant can migrate towards the surface and work its way out through the skin, causing infection, swelling, and pain. These implants have, in some cases, resulted in erosive osteoarthritis of the condyle, and are capable of perforating as a result of friction from the condyle.
Autologous grafts have also been tried. One type is a dermal graft donated from the skin of the thigh and used as a disc, or as a cap over the condyle, or as a cap over a repaired disc. Another type is the repositioned tendon of the temporalis muscle. Neither procedure has been clinically successful. The dermal graft may form cysts from hair follicles or may perforate. Both types subject that joint to excessive fibrous tissue formation which may cause a fibrous ankylosis.
The newest type of TM Joint surgery is arthroscopy, or microsurgery, performed through a cannula. By its nature, this procedure has limitations and as yet is unpredictable.
The conclusion in the field of TM Joint surgery at present is that removal of the disc without replacement is preferred due to lack of a suitable replacement. However, an implant of a TM Joint disc is more desirable because a disc maintains a stable joint, provides stable dental occlusion and avoids the possibility of osteoarthritic changes that can occur in a functioning joint without a disc.